A station for extending functions has been hitherto utilized. This station can be mounted with an extension board and a floppy disk unit/a hard disk unit, which can extend ability or enhance performance of a personal computer of the notebook type by connecting it with the notebook type personal computer.
By the way, when a personal computer of the notebook type is mounted on this station, it is necessary that an electric power source at the notebook type personal computer side is infallibly cut off. If the station is connected with the notebook type personal computer of which the electric power source is turned on, such problems as data of a program during execution become extinct, or IC is destroyed due to difference in voltage between a contained battery of the notebook type personal computer and a domestic electric power source of the notebook type personal computer. In addition, the same problems also take place when the notebook type personal computer is separated from the station in a state in which the electric power source is turned on.